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   <TITLE> Zoltan Developer's Guide:  Adding Load-Balancing Functions</TITLE>
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<div ALIGN=right><b><i><a href="dev.html">Zoltan Developer's Guide</a>&nbsp; |&nbsp; <a href="dev_add_struct.html">Next</a>&nbsp; |&nbsp; <a href="dev_add_interface.html">Previous</a></i></b></div>


<H2>
<A NAME="new_implementation"></A>Load-Balancing Function Implementation</H2>
The new load-balancing algorithm should be implemented as an <B>ZOLTAN_LB_FN</B>.
The type definition for an <B>ZOLTAN_LB_FN</B> is in <I>lb/lb_const.h</I> and
is described below. When the new algorithm is selected,
the <I>LB_Fn</I> field of the <B>Zoltan_Struct</B> is set to point to the <B>ZOLTAN_LB_FN</B>
function for the new algorithm. This pointer is then used in invoking load
balancing in <B><A HREF="../ug_html/ug_interface_lb.html#Zoltan_LB_Partition">Zoltan_LB_Partition</A></B>.
<BR>&nbsp;

<P>
<hr>
<HR>typedef int <B>ZOLTAN_LB_FN</B>
(struct&nbsp;<B><A HREF="dev_lb_structs.html#Zoltan_Struct">Zoltan_Struct</A></B>&nbsp;*<I>zz</I>,
float&nbsp;*<I>part_sizes</I>,
int&nbsp;*<I>num_import</I>,
<B><A HREF="dev_lb_types.html">ZOLTAN_ID_PTR</A></B>&nbsp;*<I>import_global_ids</I>,
<B><A HREF="dev_lb_types.html">ZOLTAN_ID_PTR</A></B>&nbsp;*<I>import_local_ids</I>,
int&nbsp;**<I>import_procs</I>,
int&nbsp;**<I>import_to_parts</I>,
int&nbsp;*<I>num_export</I>,
<B><A HREF="dev_lb_types.html">ZOLTAN_ID_PTR</A></B>&nbsp;*<I>export_global_ids</I>,
<B><A HREF="dev_lb_types.html">ZOLTAN_ID_PTR</A></B>&nbsp;*<I>export_local_ids</I>,
int&nbsp;**<I>export_procs</I>,&nbsp;
int&nbsp;**<I>export_to_parts</I>);&nbsp;
<HR>
<BR>The <B>ZOLTAN_LB_FN</B> function type describes the arguments passed to a
load-balancing function. The input to the function is a <B><A HREF="dev_lb_structs.html#Zoltan_Struct">Zoltan_Struct</A></B>
containing pointers to application-registered functions to be used in the
load-balancing algorithm. The remaining arguments are output parameters
listing the objects to be imported or exported to the processor in the
new decomposition. The arrays for global and local IDs and source processors
must be allocated by the load-balancing function. The load-balancing function
may return either the import arrays, the export arrays, or both. If no
import data is returned, *<I>num_import </I>must be set to a negative number,
and similarly with *<I>num_export.</I>
Full support of the <a href="../ug_html/ug_alg.html#RETURN_LISTS">RETURN_LISTS</a>
parameter is not required. 
If <a href="../ug_html/ug_alg.html#RETURN_LISTS">RETURN_LISTS</a>
is not set to NONE,
the new algorithm may return either import or export lists; the Zoltan
interface will then build the lists requested by
<a href="../ug_html/ug_alg.html#RETURN_LISTS">RETURN_LISTS</a>.

<BR>&nbsp;
<TABLE WIDTH="100%" >
<TR VALIGN=TOP>
<TD VALIGN=TOP WIDTH="20%"><B>Arguments:</B></TD>

<TD WIDTH="80%"></TD>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP><I>&nbsp;&nbsp;&nbsp; zz</I></TD>

<TD>A pointer to the <B><A HREF="dev_lb_structs.html#Zoltan_Struct">Zoltan_Struct</A></B>
to be used in the load-balancing algorithm.</TD>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP><I>&nbsp;&nbsp;&nbsp; part_sizes</I></TD>

<TD>Input:  an array of part sizes for each weight component.
Entry 
<i>part_sizes[i*obj_weight_dim+j]</i>
contains the user-requested 
part size for part <i>i</i> with respect to object weight <i>j</i> for
<i>i</i>=0,1,...,number of parts-1, and 
<i>j</i>=0,1,...,<i>obj_weight_dim</i>-1.
If the application sets parameter 
<i><a href="../ug_html/ug_param.html#OBJ_WEIGHT_DIM">OBJ_WEIGHT_DIM</a></i>,
<i>obj_weight_dim</i> is the set value of 
<i><a href="../ug_html/ug_param.html#OBJ_WEIGHT_DIM">OBJ_WEIGHT_DIM</a></i>;
otherwise, <i>obj_weight_dim</i> is one.
</TD>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP><I>&nbsp;&nbsp;&nbsp; num_import</I></TD>

<TD>Upon return, the number of objects to be imported to the processor
for the new decomposition. A negative number indicates that no import data
has been computed and the import arrays should be ignored.</TD>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP><I>&nbsp;&nbsp;&nbsp; import_global_ids</I></TD>

<TD>Upon return, an array of <I>num_import</I> global IDs
of objects to be imported to the processor for the new decomposition.
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP>&nbsp;&nbsp;&nbsp; <I>import_local_ids</I></TD>

<TD>Upon return, an array of <I>num_import</I> local IDs
of objects to be imported to the processor for the new decomposition.
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP>&nbsp;&nbsp;&nbsp; <I>import_procs</I></TD>

<TD>Upon return, an array of size <I>num_import</I> containing the processor
IDs of processors owning (in the old decomposition) the objects to be imported
for the new decomposition.
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP>&nbsp;&nbsp;&nbsp; <I>import_to_parts</I></TD>

<TD>Upon return, an array of size <I>num_import</I> containing the part
IDs of parts to which objects will be imported
 <i>in the NEW decomposition</i>.
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>
<TR VALIGN=TOP>
<TD>&nbsp;&nbsp;&nbsp; <I>num_export</I></TD>

<TD>Upon return, the number of objects to be exported from the processor
for the new decomposition. A negative number indicates that no export data
has been computed and the export arrays should be ignored.</TD>
</TR>

<TR VALIGN=TOP>
<TD>&nbsp;&nbsp;&nbsp; <I>export_global_ids</I></TD>

<TD>Upon return, an array of <I>num_export</I> global IDs
of objects to be exported from the processor for the new decomposition.
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>

<TR VALIGN=TOP>
<TD>&nbsp;&nbsp;&nbsp; <I>export_local_ids</I></TD>

<TD>Upon return, an array of <I>num_export</I> local IDs
of objects to be exported from the processor for the new decomposition.
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</TD>
</TR>

<TR VALIGN=TOP>
<TD>&nbsp;&nbsp;&nbsp; <I>export_procs</I></TD>

<TD>Upon return, an array of size <I>num_export</I> containing the
processor IDs of processors owning (in the old decomposition) the objects
to be exported for the new decomposition.&nbsp;
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>
<TR VALIGN=TOP>
<TD>&nbsp;&nbsp;&nbsp; <I>export_to_parts</I></TD>

<TD>Upon return, an array of size <I>num_export</I> containing the
part IDs of parts to which the objects will be 
exported for the new decomposition.&nbsp;
If this array is non-null, it must be allocated by 
<b><a href="dev_add_memory.html#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
</td>
</TR>

<TR VALIGN=TOP>
<TD></TD>

<TD></TD>
</TR>

<TR VALIGN=TOP>
<TD><B>Returned Value:</B></TD>

<TD></TD>
</TR>

<TR VALIGN=TOP>
<TD VALIGN=TOP>&nbsp;&nbsp;&nbsp; int</TD>

<TD><A HREF="../ug_html/ug_interface.html#Error Codes">Error code</A>.</TD>
</TR>
</TABLE>

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